Simple MVC NerdDinners Lambda

Question

In this code from Microsoft's MVC Tutorial NerdDinners:

public class DinnerRepository {

private NerdDinnerDataContext db = new NerdDinnerDataContext();

//
// Query Methods

public IQueryable<Dinner> FindAllDinners() {
    return db.Dinners;
}

public IQueryable<Dinner> FindUpcomingDinners() {
    return from dinner in db.Dinners
           where dinner.EventDate > DateTime.Now
           orderby dinner.EventDate
           select dinner;
}

public Dinner GetDinner(int id) {
    return db.Dinners.SingleOrDefault(d => d.DinnerID == id);
}

//
// Insert/Delete Methods

public void Add(Dinner dinner) {
    db.Dinners.InsertOnSubmit(dinner);
}

public void Delete(Dinner dinner) {
    db.RSVPs.DeleteAllOnSubmit(dinner.RSVPs);
    db.Dinners.DeleteOnSubmit(dinner);
}

//
// Persistence 

public void Save() {
    db.SubmitChanges();
} 

}

What does:

public Dinner GetDinner(int id) {
    return db.Dinners.SingleOrDefault(d => d.DinnerID == id);
}

the "d" mean? How does this code work? I know it it bringing back dinners where dinnerid matches id from the function parameter. I don't understand the "d goes to..." means. I know it is a lambda but I don't really get it. What is the "d" for? What does it do?

Could this have been written without the lambda here (how)?

Answer 1

You should probably read up on anonymous methods.

Basically the code you are referring to can be written as an anonymous method without lamba syntax like this:

public Dinner GetDinner(int id) {    
   return db.Dinners.SingleOrDefault(delegate (Dinner d) {
                                       return d.DinnerID == id;
                                     });
}

Answer 2

This is similar too...

from d in db.Dinners
where d.DinnerID == id
select d

The code basically loops around the dinners returning the first Dinner or the default if none is found.

This is a case where the naming conventions used in a sample aren't always appropriate in production. Using a "d" as a local variable is usually fround upon and choosing a variable name of "dinner" would probably be more appropriate, although in this case the scope of d is so small it is clear either way, as long as you know how lambda expressions work.